1. Field Of Invention
This invention is directed toward developing a high frequency economical electronic ballast having high power factor, low device stresses, high frequency, low switching losses, and sine wave output for lighting nonlinear loads such as HID lamps, more specifically metal halide lamps and also to provide plurality of the lamp connections for the lighting industry in general.
2. Description Of The Prior Art
The contemporary high frequency electronic ballasts used for lighting purposes use either boost converter or a flyback converter in discontinuous mode for controlling the power factor, and to pre-regulate the DC voltage connected to the inverter. Bandel, in his U.S. Pat. No. 5,359,274, uses boost converter for power factor correction. Mortimer et. al. in their U.S. Pat. No. 5,204, 587 uses flyback PWM converter in discontinuous mode to correct the power factor. Also, use Mapham inverter or Shwartz inverter, or their modifications having half bridge or fall bridge configurations. The prior art Mapham inverter is described by Neville Mapham in IEEE Transactions on Industry and General Applications, March/April 1967, IGA-2, No. 2, pages 176-187. Mapham showed an SCR inverter with a good regulation and a sine wave output which provides a frequency dependent output voltage, such as shown in FIG. 1. U.S. Pat. No. 4,220,896 by Derek A. Paice describes a ballast filter which reduces the KVA ratings of the transformer. But in the above mentioned prior art, only the voltage ratings of the transformer are reduced by quality factor times four times the ballast filter. The current ratings of the transformer are increased as it has to take care of the filter capacitor current. Thus, insulation requirements of the transformer are reduced at the cost of increased copper losses in the transformer. From the switch point of view voltage ratings of the switches are reduced, making them economical.
The converters used for power factor correction in the contemporary art had the drawbacks of either forcing high voltage on the inverter switches, or it produced the discontinuous current at the input, thus contributing to EMI/RFI produced. Also the switches used in the prior art inverters have high on losses. This is because the switches have to support the additional current drawn by the capacitor connected in parallel with the transformer primary. For proper operation of the Mapham inverter, a value of the capacitor should be such that it draws at least four times the instantaneous load current.